1. Field of the Invention
The present invention relates to a piezoelectric actuator used for, for example, an ink jet printing head. More particularly, this invention relates to a method for manufacturing a piezoelectric actuator, concerning which the internal stress is extremely relaxed, and which permits upsizing of a head, and also relates to a product made by such a manufacturing method.
2. Description of the Related Art
A piezoelectric actuator is a device having an electromechanical transducing function and is composed of crystallized piezoelectric ceramic. As a method for manufacturing this piezoelectric actuator, generally employed is a so-called sol-gel method of applying a sol of organometallic compound over an electrode, drying and pyrolysing the sol, and giving high temperature treatment to cause crystallization, which is followed by a method of causing instant crystallization with high heat.
By another crystallization method which is called a xe2x80x9chydrothermal method,xe2x80x9d a Ti or Ni substrate is dipped in a KOH solution containing organometallic compound, thereby causing PZT grains to deposit.
However, when the piezoelectric actuator is manufactured by the sol-gel method, there is a problem in that thermal stress occurs and cracks are easily made in a piezoelectric film. Accordingly, it has been difficult to manufacture a piezoelectric actuator with a large area. For example, it has been impossible to manufacture a piezoelectric actuator for a line printer.
Moreover, a piezoelectric actuator manufactured by the conventional hydrothermal method has a rough surface and, therefore, it has been difficult to make an upper electrode in good contact with the piezoelectric actuator.
The research paper on xe2x80x9cApplication of Hydrothermal Mechanism for Tailor-making Perovskite Titanate Films,xe2x80x9d IEEE Proc. of the 9th International Symposium on Electrets, Shanghai, China (held on September 25 through September 30) (pp. 617-622) (1996), which was prepared by W-ping Xu, Masanori Okuyama, et al., describes a method of causing a precursor film of piezoelectric ceramic to crystallize by putting the precursor film, which has been applied over a substrate and has been dried, in a given alkaline solution. This method of causing crystallization in an alkaline solution is called the hydrothermal method. This hydrothermal method enables the crystallization at comparatively lower temperatures than in the case of the sol-gel method, thereby giving rise to several advantages. For example, since the low temperature manufacturing results in less internal stress, including thermal stress, generated in the film in the course of crystallization, it is considered to be possible to form a piezoelectric film with a larger area than a conventional piezoelectric film.
The above-mentioned research paper states that an alkaline treatment solution is used for the hydrothermal treatment.
However, there is a problem in that silicon, which is suitable for fine processing as a material for a pressure chamber substrate, or the piezoelectric film layer itself is easily soluble in a strong alkaline treatment solution such as KOH. Therefore, when silicon is used for the substrate, it is necessary to use a weak alkaline solution prepared by adding Ba, such as barium hydroxide, to the strong alkaline solution, or to adjust treatment conditions. Particularly, when it is necessary to apply fine processing to a substrate for which silicon is used, even the use of the weak alkaline treatment solution containing Ba may cause slight erosion and, therefore, it is considered to cause inconvenience. It is desirable that the alkaline degree of the treatment solution be as low as possible.
Moreover, the above-mentioned research paper does not include sufficient descriptions about the manufacture of a piezoelectric actuator with good characteristics, which is suitable for an ink jet printing head for a printer.
In consideration of the above-described inconveniences and as a result of numerous experiments, the inventors of this application have found the hydrothermal treatment which causes little erosion.
Moreover, the inventors carried out experiments on the manufacture of piezoelectric actuators by the hydrothermal method, specifically on the conditions for manufacturing the entire piezoelectric actuators, including the application of a sol composed of organometallic compound, and then have found the manufacturing method appropriate for the practice of the above-mentioned hydrothermal method.
Namely, it is an object of this invention to provide a piezoelectric actuator which can be made with a large area and which has a crystal structure with flat surfaces.
It is another object of this invention to provide an ink jet printing head which is suitable for a line printer and which comprises a piezoelectric actuator that can be made with a large area and with a flat surface.
It is a still another object to provide a printer which comprises an ink jet printing head suitable for a line printer.
It is a further object to provide a method for manufacturing a piezoelectric actuator concerning which there is a wide selection of possible materials and options for manufacture conditions, and which has good performance.
It is a still further object to apply the above-mentioned method for manufacturing the piezoelectric actuator and to provide a method for manufacturing an ink jet printing head concerning which there is a wide selection of possible materials and options for manufacture conditions, and which has good performance.
Specifically speaking, this invention provides a piezoelectric actuator which comprises: a lower electrode; an upper electrode; and a piezoelectric film held between the lower electrode and the upper electrode, wherein the piezoelectric film is made of piezoelectric ceramic, and columnar crystal grains of the piezoelectric ceramic are random-oriented in a film thickness direction and a mean diameter of the columnar crystal grains is in the range of 100 nm to 15000 nm.
It is desirable that a mean diameter of the columnar crystal grains be in the range of 100 nm to 10000 nm.
The surface roughness of the upper electrode side of the piezoelectric film can be set at 20 nm or less as a maximum height.
The element composition of the piezoelectric film can include any one of the following piezoelectric ceramic materials among lead zirconate titanate (Pb(Zr,Ti)O3:PZT), lead lanthanum titanate ((Pb,La)TiO3), lead lanthanum zirconate ((Pb,La)ZrO3), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O3:PLZT), and lead magnesium niobate zirconate titanate (Pb(Mg,Nb)(Zr,Ti)O3:PMN-PZT).
Moreover, this invention provides an ink jet printing head with a piezoelectric actuator according to this invention, and such an ink jet printing head comprises: a pressure chamber substrate with a pressure chamber formed therein; a diaphragm provided on one side of the pressure chamber; and the piezoelectric actuator provided on the diaphragm at the position corresponding to the pressure chamber, wherein the piezoelectric actuator is composed to be capable of causing volume changes of the pressure chamber.
This invention also provides a printer with the above-described ink jet printing head according to this invention, and such a printer comprises: a recording medium carrying mechanism composed to be capable of supplying and taking out the recording media; and a head control circuit for causing the ink jet printing head to print at any position on the recording medium supplied by the recording medium carrying mechanism.
This invention further provides a printer with the above-described ink jet printing head according to this invention, and such a printer comprises: a recording medium carrying mechanism composed to be capable of supplying and taking out the recording media; and a head carrying mechanism for carrying the ink jet printing head to any position on the recording medium supplied by the recording medium carrying mechanism.
Furthermore, this invention provides a method for manufacturing a piezoelectric actuator comprising a piezoelectric film held between a lower electrode and an upper electrode, wherein the method comprises the steps of: forming a precursor film in an amorphous state, containing metal and oxygen, over the lower electrode; and giving hydrothermal treatment to the precursor film by dipping the precursor film in a given alkaline solution and promoting the crystallization under certain conditions.
As the above-described alkaline solution, a solution adjusted to contain an alkaline solute of concentration not higher than 2 M[mol/l] can be used. Preferably, a solution adjusted to contain the alkaline solute of concentration not higher than 0.5 M[mol/l] should be used. More preferably, a solution adjusted to contain the alkaline solute of concentration not higher than 0.1 M[mol/l] should be used. Most preferably, a solution adjusted to contain the alkaline solute of concentration not higher than 0.05 M[mol/l] should be used.
In the step of forming the precursor film, the precursor film in the amorphous state can be formed by applying a sol containing organometallic compound over the lower electrode and by heating it.
Moreover, the step of forming the precursor film can comprise the steps of: applying a precursor composed of organometallic compound; drying the precursor at a given temperature; pyrolysing the precursor at temperatures ranging from 300xc2x0 C. to 500xc2x0 C.
The alkaline solution can be selected from the group consisting of KOH, Ba(OH)2, Pb(OH)2, Ba(OH)2+Pb(OH)2, KOH +Ba(OH)2, and KOH+Pb(OH)2.
In the pyrolysing step, the precursor can be degreased at a temperature of 450xc2x0 C.
In the drying step, the precursor can be dried at temperatures ranging from 150xc2x0 C. to 200xc2x0 C.
In the step of forming the precursor, the precursor film in the amorphous state containing metal and oxygen can be formed by any one of the following methods among an RF sputtering method, an ion beam sputtering method, and an electron beam deposition method.
The certain conditions in the hydrothermal treatment step can be set at temperatures ranging from 100xc2x0 C. to 200xc2x0 C. and at 10 or lower atmospheric pressure.
The certain conditions in the hydrothermal treatment step can be set at a temperature of 140xc2x0 C. and at 4 atmospheric pressure.
By the method for manufacturing a piezoelectric actuator according to this invention, the step of applying the precursor, the step of drying the precursor, and the step of pyrolysing the dried precursor can be repeated at least once.
In the step of forming the precursor, the step of applying the organometallic compound solution, the step of drying a film of organometallic compound, which is formed by the application, at a first temperature, and the step of pyrolysing the dried organometallic compound film at a second temperature can be repeated at least once.
Furthermore, this invention provides a method for manufacturing an ink jet printing head comprising a piezoelectric actuator manufactured by the above-described manufacturing method according to this invention, and such a method for manufacturing an ink jet printing head comprises the steps of: forming a diaphragm on one side of a substrate; manufacturing the piezoelectric actuator on the diaphragm; and forming a pressure chamber by etching the substrate in such arrangement that the diaphragm with the piezoelectric actuator provided thereon forms one side of the pressure chamber.